This invention resides broadly in the field of keyboard musical instruments and is particularly adaptable for use in electronic or pipe organs as a system for producing what is commonly known as "tracker touch" for the keys.
In a mechanical action pipe organ, which is sometimes known as a tracker action, the "feel" of the keys is characterized by an initial resistance as the key is depressed. As the key is depressed farther downward, it "drops" or "toggles" so that as the key travels through its complete distance and just before it rests on the key bed noticeable reduction in the pressure or force needed to depress the key is apparent to the player. This results in a feel which is prized by many keyboard musicians and organists.
The function of a key in a keyboard musical instrument, e.g., an organ, is to allow the musician to effectively control, by a playing technique, the duration of the tones that are developed by the keyboard musical instrument. This will be true whether the instrument is an organ using traditional pipes or an electronic musical instrument simulating the sound of a pipe organ. Generally speaking, in keyboard musical instruments, such as organs, which do not have mechanical actions with an inherent tracker touch, a tension spring is supplied to return the key to its normal position. Tracker touch arrangements have been devised for such instruments to replace this simple spring arrangement. Some of these arrangements have included the use of magnets. Others have utilized torsion springs of various sorts which are mounted in offset positions so that as the key is depressed, a toggling effect is produced.
Some examples of those torsion springs which have been used are described immediately following. In a Casavant pipe organ a "grasshopper" spring was used to achieve the desired toggling effect. The grasshopper spring was mounted to a brass pin in a slot on the key tail and secured by a hook arrangement on the end of one leg of the spring. The other leg of the spring is bent outward toward its end and is positioned in a "dent" in a horizontal metal bar mounted along the rear edge of the key bed. The position of the dent in the bar was such that it allowed the spring to move or "toggle" without physically stroking the bar as the key was depressed.
Another method for achieving the tracker action was what may be called the Holtkamp system. A pointed metal stamping was held by a pin in a slot in the key tail at an upward angle. The distal end of the metal stamping, when the key was in its normal position, rested in a dent or depression in a spring fastened to the key bed, extending vertically upward therefrom. As the key was depressed, the metal stamping bent slightly as it was retained within the depression on the spring until the spring force was exceeded and the pin moved upward away from the depression, thus achieving the desired toggling effect.
Another method of achieving the tracker action "feel" was that put forth by Aeolian-Skinner. Towards the front of the key a spring made of a phosphor-bronze alloy was held in a fixed position on the underside of the key by an adjustable screw. This spring had a bend in its distal end with a depression in the bent portion. A grasshopper spring was held in a slot of the front pin rail in a fixed position while its other end was aligned with the depression in the phosphor-bronze spring when the key was in its normal position. As the key was depressed, the two springs would interact until their spring forces were exceeded and the grasshopper spring would toggle, thus reducing the necessary downward force on the key and achieving the desired tracker touch.
Another method was devised by E. M. Skinner. This was done by attaching a curved steel spring to the underside of the front pin rail, permitting the curved portion of the spring to extend upwards. The distal end of the curved steel spring included a depression for accommodating one end of a steel pin. Near the front end of the key and in close proximity to the curved spring an adjustable pin is located extending downward from the underside of the key. The pin had several detents or depressions located around its circumference at different distances from the underside of the key. This is so that the necessary force to achieve the toggling effect may be adjusted to be greater or lesser at the option of the player. Extending between the downward extending pin and the curved spring is a steel pin having points at both of its ends to fit into the depression of the spring and the detent in the pin. The steel pin is held in place by the spring force from the spring. With the key in the normal position the steel pin is inclined slightly upward towards the downward extending pin and, as the key is depressed, the pin travels downward causing the pin to achieve a horizontal position. At or near this horizontal position the toggling effect is achieved due to the downward force exceeding the spring force. The spring then adds to the downward pressure on the key as the detent in the downward extending pin is forced below the level of the depression in the curved spring so that the steel pin is now inclined downward to the rear of the key bed. This interaction applies additional force to the depressing of the key. Upon key release the spring components return to their normal position with the steel pin being inclined slightly upward towards the rear of the key bed. It should be noted that the steel pin remains in the depression of the curved spring and in the selected detent of the downwardly extending pin at all times.
The problems with the above-described spring arrangements are that they invariably get out of adjustment as they are used over a period of time. This is caused by the wearing of the mechanical parts and due to such wear the change in the spring factor resulting in a change, i.e., a decrease, in the spring force which achieves the desired "toggling" of the tracker touch. Thus the feel which is so prized by the keyboard musician is lost completely or distorted which makes this playing technique unmanageable.
It is an object of this invention to eliminate the necessity of the complicated mechanical interaction of the spring mechanisms of the prior attempts to achieve the desired effect and to substitute therefor a simple mechanism not subject to the constant wear and adjustment necessitated by the prior mechanisms.
Other objects will appear hereinafter.